The R-domain and exon 0 are conserved across vertebrates.

<p>Vertebrate exon 0 sequence alignment including human, chimp, mouse, rat, dog, horse, platypus and zebrafish. The consensus track indicates residues conserved among all species with an asterisk (*) and those conserved in all higher vertebrates with a circumflex accent (∧). The nucleotide sequence of the R-domain including the translation is shaded; the translational start codon in underlined. The genomic locations of the aligned sequences are: UCSC version hg18, March 2006, chr21:45,396,913–45,397,066 (Homo sapiens); UCSC version panTro2, March 2006, chr21:44,799,898–44,800,051 (Pan troglodytes); UCSC version mm8, February 2006, chr10:76,783,722–76,783,879 (Mus musculus); UCSC version rn4, November 2004, chr20:11,691,863–11,692,020 (Rattus norvegicus); UCSC version canFam2, May 2005, chr31:41,072,028–41,072,166 (Canis familiaris); UCSC version equCab1, February 2007, chr26:1,562,280–1,562,433 (Equus caballus); UCSC version ornAna1, March 2007, Ultra489:519,316–519,487 (Ornithorhychus anatinus); and NCBI assembly Zv7, July 2008, Chromosome 22, NW_001878325.1 (Danio rerio).